1. Technical Field
The present invention relates to a vacuum pump and a mass spectrometer.
2. Background Art
Vacuum pumps such as turbo-molecular pumps have been used for various devices as the pumps being able to generate clean high-vacuum environment. An example of these devices is a mass analyzer. In the mass analyzer, the degree of vacuum in a quadrupole rod or a detector is set at about five to ten times higher than the degree of vacuum in an ion source. For this reason, a vacuum pump provided with a plurality of suction ports has been known so that a single vacuum pump is applicable to the above-described devices (see, e.g., Patent Literature 1 (JP-A-2003-129990)).
The vacuum pump described in Patent Literature 1 includes first and second turbo-molecular stages and a Holweck stage. Such a pump further includes a first suction port for a flow into the first turbo-molecular stage, a second suction port for a flow in between the first and second turbo-molecular stages, and a third suction port for a flow into the Holweck stage. A through-hole communicating with the third suction port is formed on a stator side of the Holweck stage.
Plural spiral grooves are formed at a stator of the Holweck stage, and gas is exhausted from each spiral groove. However, in the vacuum pump described in Patent Literature 1, the through-hole penetrates through only some of the spiral grooves, and for this reason, a gas flow rate varies among the spiral grooves. As a result, the suction-side pressure of the Holweck stage increases, leading to worse exhaust performance of the entire pump.